ORURO, Bolivia, Dec 9 (Reuters) - An assembly boycotted by the rightist
opposition to Bolivian President Evo Morales approved most of a controversial
new constitution he supports during an all-night session guarded by miners
and peasant farmers.

The assembly dominated by delegates from Morales' Movement Toward Socialism,
or MAS, party, on Saturday and Sunday approved changes that would allow
two consecutive five-year terms for presidents, greater state control of
the economy, and more autonomy for provinces and indigenous communities.

"We're coming to a happy ending, we're managing to approve the new
constitution the Bolivian people are asking for," said Roman Loayza,
head of the MAS delegates in the assembly after 13 hours of voting in a
university auditorium in Oruro, 140 miles (230 km) south of La Paz. More
than 400 changes were approved.

But several steps are necessary before the constitution can be enacted.
First, a nationwide referendum is needed on one remaining article. Then,
the assembly will vote on the entire text. Finally, another nationwide
referendum is required on the full constitution.

The assembly was moved to Oruro after three people were killed two weeks
ago in violent protests against the process in Sucre, where it had been
meeting for months.

As the assembly voted on Saturday night and Sunday morning, miners and
peasant farmers loyal to Morales guarded the university auditorium where
the session was being held. They exploded small dynamite charges occasionally
to intimidate any potential anti-assembly protesters.

Morales said he was very happy with the vote.

"They accused us of seeking reelection for an indefinite period,
but now we've demonstrated it's not like that," he told reporters.
Under current Bolivian law, presidents cannot run for reelection until
they've been out of office at least one term.

OPPOSITION BOYCOTT

The assembly also approved articles requiring election rather than appointment
of top judges, and transforming the voting mechanism for the upper house
of Congress, which is currently controlled by the opposition.

Bolivia's poor, indigenous majority has clamored for a new constitution
and forming one was a key campaign promise of Morales, the country's first
president of indigenous descent.

But the overhaul of the constitution has widened the rift between the
mountainous, largely poor and indigenous part of the country that backs
Morales, and the relatively wealthy western lowlands, where the opposition
has greater force.

Of the assembly's 255 delegates more than one third boycotted Saturday's
session, including Bolivia's two biggest right and center-right parties,
which decry the process as a Morales power grab.

Opposition delegates said they would challenge the new constitution, which
they said was approved illegally.

"Every legal rule has been violated. This constitution is illegal
and we'll denounce it in every forum we can," Boris Medina, delegate
from the rightist Podemos party, told La Razon newspaper.

Guillermo Richter, a delegate from the center-right Revolutionary Nationalist
Movement, said he felt "huge frustration because the new Magna Carta
is being approved in an illegal way and without a big national agreement."

The assembly left one article -- a technical definition of unproductive
land holdings -- for a nationwide referendum, apparently in a political
maneuver that will make it easier to get the entire text ratified in the
assembly early next year.

Morales is an ally of Venezuela's Hugo Chavez, whose own constitutional
reform project was defeated narrowly in a referendum last weekend. Another
ideological ally, Ecuador's Rafael Correa, is also pushing changes to his
country's constitution.